[ADD] common: ship a standard .gitignore to all repos

The pre-commit workflow runs
``git ls-files --others --exclude-from=.gitignore`` to detect files
generated by hooks that are not committed. This aborts with
"cannot use .gitignore as an exclude file" in repos that have no root
.gitignore (all Elabore addons repos).

Ship the OCA-standard .gitignore via config/common so every repo has one.

config/common/.gitignore

@@ -0,0 +1,88 @@
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+/.venv
+/.pytest_cache
+/.ruff_cache
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+env/
+bin/
+build/
+develop-eggs/
+dist/
+eggs/
+lib64/
+parts/
+sdist/
+var/
+*.egg-info/
+.installed.cfg
+*.egg
+*.eggs
+
+# Windows installers
+*.msi
+
+# Debian packages
+*.deb
+
+# Redhat packages
+*.rpm
+
+# MacOS packages
+*.dmg
+*.pkg
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.coverage
+.cache
+nosetests.xml
+coverage.xml
+
+# Translations
+*.mo
+
+# Pycharm
+.idea
+
+# Eclipse
+.settings
+
+# Visual Studio cache/options directory
+.vs/
+.vscode
+
+# OSX Files
+.DS_Store
+
+# Django stuff:
+*.log
+
+# Mr Developer
+.mr.developer.cfg
+.project
+.pydevproject
+
+# Rope
+.ropeproject
+
+# Sphinx documentation
+docs/_build/
+
+# Backup files
+*~
+*.swp
+
+# OCA rules
+!static/lib/